Many current medicines suffer from poor absorption, distribution, metabolism and/or excretion (ADME) properties that prevent their wider use. Poor ADME properties are also a major reason for the failure of drug candidates in clinical trials. While formulation technologies and prodrug strategies can be employed in some cases to improve certain ADME properties, these approaches often fail to address the underlying ADME problems that exist for many drugs and drug candidates. One such problem is rapid metabolism that causes a number of drugs, which otherwise would be highly effective in treating a disease, to be cleared too rapidly from the body. A possible solution to rapid drug clearance is frequent or high dosing to attain a sufficiently high plasma level of drug. This, however, introduces a number of potential treatment problems such as poor patient compliance with the dosing regimen, side effects that become more acute with higher doses, and increased cost of treatment.
In some select cases, a metabolic inhibitor will be co-administered with a drug that is cleared too rapidly. Such is the case with the protease inhibitor class of drugs that are used to treat HIV infection. The FDA recommends that these drugs be co-dosed with ritonavir, an inhibitor of cytochrome P450 enzyme 3A4 (CYP3A4), the enzyme typically responsible for their metabolism (see Kempf, D. J. et al., Antimicrobial agents and chemotherapy, 1997, 41(3): 654-60). Ritonavir, however, causes adverse effects and adds to the pill burden for HIV patients who must already take a combination of different drugs. Similarly, the CYP2D6 inhibitor quinidine has been added to dextromethorphan for the purpose of reducing rapid CYP2D6 metabolism of dextromethorphan in a treatment of pseudobulbar affect. Quinidine, however, has unwanted side effects that greatly limit its use in potential combination therapy (see Wang, L et al., Clinical Pharmacology and Therapeutics, 1994, 56(6 Pt 1): 659-67; and FDA label for quinidine at www.accessdata.fda.gov).
In general, combining drugs with cytochrome P450 inhibitors is not a satisfactory strategy for decreasing drug clearance. The inhibition of a CYP enzyme's activity can affect the metabolism and clearance of other drugs metabolized by that same enzyme. CYP inhibition can cause other drugs to accumulate in the body to toxic levels.
A potentially attractive strategy for improving a drug's metabolic properties is deuterium modification. In this approach, one attempts to slow the CYP-mediated metabolism of a drug by replacing one or more hydrogen atoms with deuterium atoms. Deuterium is a safe, stable, non-radioactive isotope of hydrogen. Compared to hydrogen, deuterium forms stronger bonds with carbon. In select cases, the increased bond strength imparted by deuterium can positively impact the ADME properties of a drug, creating the potential for improved drug efficacy, safety, and/or tolerability. At the same time, because the size and shape of deuterium are essentially identical to those of hydrogen, replacement of hydrogen by deuterium would not be expected to affect the biochemical potency and selectivity of the drug as compared to the original chemical entity that contains only hydrogen.
Over the past 35 years, the effects of deuterium substitution on the rate of metabolism have been reported for a very small percentage of approved drugs (see, e.g., Blake, M I et al, J Pharm Sci, 1975, 64:367-91; Foster, A B, Adv Drug Res 1985, 14:1-40 (“Foster”); Kushner, D J et al, Can J Physiol Pharmacol 1999, 79-88; Fisher, M B et al, Curr Opin Drug Discov Devel, 2006, 9:101-09 (“Fisher”)). The results have been variable and unpredictable. For some compounds deuteration caused decreased metabolic clearance in vivo. For others, there was no change in metabolism. Still others demonstrated increased metabolic clearance. The variability in deuterium effects has also led experts to question or dismiss deuterium modification as a viable drug design strategy for inhibiting adverse metabolism (see Foster at p. 35 and Fisher at p. 101).
The effects of deuterium modification on a drug's metabolic properties are not predictable even when deuterium atoms are incorporated at known sites of metabolism. Only by actually preparing and testing a deuterated drug can one determine if and how the rate of metabolism will differ from that of its non-deuterated counterpart. See, for example, Fukuto et al. (J. Med. Chem. 1991, 34, 2871-76). Many drugs have multiple sites where metabolism is possible. The site(s) where deuterium substitution is required and the extent of deuteration necessary to see an effect on metabolism, if any, will be different for each drug.
This invention relates to novel substituted dioxopiperidinyl phthalimide derivatives and pharmaceutically acceptable salts thereof. The invention also provides compositions comprising a compound of this invention and the use of such compositions in methods of treating diseases and conditions beneficially treated by an immunomodulatory agent.
Lenalidomide, chemically known as either 3-(4-amino-1,3-dihydro-1-oxo-2H-isoindol-2-yl)-2,6-piperidinedione or 3-(4-amino-1-oxo 1,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione, and its pharmaceutically acceptable salts thereof are disclosed as immunomodulatory agents. Lenalidomide has been shown to inhibit the secretion of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and to increase the secretion of anti-inflammatory cytokines in animals and humans. Decreasing TNF-α levels is a valuable therapeutic strategy for the treatment of many inflammatory, infectious, immunological, and malignant diseases (PCT publication WO 98/03502). Lenalidomide has been demonstrated to be useful in the treatment of anemia due to myelodysplastic syndromes associated with a deletion 5q cytogenic abnormality, as well as in the treatment of multiple myeloma when used in combination with dexamethasone. (http://www.fda.gov/cder/foi/label/2006/021880s001.pdf).
Lenalidomide is also in clinical trials, alone or in combination with other therapeutic agents, for the treatment of Non-Hodgkins lymphoma; papillary and follicular thyroid carcinoma; prostate cancer; chronic lymphocytic leukemia, amyloidosis, complex regional pain syndrome Type I, malignant melanoma, radiculopathy, myelofibrosis, glioblastoma, gliosarcoma, malignant gliomas, myelogenous leukemia, refractory plasma cell neoplasm, chronic myelomonocytic leukemia, follicular lymphoma, ciliary body and chronic melanoma, iris melanoma, recurrent interocular melanoma, extraocular extension melanoma, solid tumors, T-cell lymphoma, erythroid lymphoma, monoblastic and monocytic leukemia; myeloid leukemia, brain tumor, meningioma, spinal cord tumors, thyroid cancers, mantle cell lymphoma, non-small cell lung cancer, ovarian cancer, prostate cancer, renal cell cancer, myelofibrosis, Burkitt's lymphoma, Hodgkin's lymphoma, large cell lymphoma, and Waldenstrom's macroglobulinemia.
Lenalidomide is associated with significant potential toxicities, which include human birth defects; neutropenia; thrombocytopenia; deep vein thrombosis; and pulmonary embolism. See (http://www.fda.gov/cder/foi/label/2006/021880s001.pdf). A majority of patients taking lenalidomide required a dose delay or reduction during clinical trials due to hematologic toxicities. No clinical studies were performed to assess the relationship between exposure and safety.
Despite the beneficial activities of lenalidomide, there is a continuing need for new compounds to treat the aforementioned diseases and conditions.